The RAPHaEL robotic hand is powered by compressed air; its elastic ligaments can grasp firmly or gently, depending on the task. RAPHaEL (which stands for Robotic Air-Powered Hand with Elastic Ligaments) was created by undergraduates at Virginia Tech's Robotics and Mechanisms Laboratory.
Watch the RAPHaEL robotic hand video to see more.
(RAPHaEL robotic hand video)
Apparently, the robotic hand is not controlled one finger joint at a time; one actuator is used to move all of a fingers joints.
"It's a very interesting and novel [method] of actuating fingers in a very simple, elegant, and low-cost way," said faculty adviser and lab director Dennis Hong.
Update 29-Sep-2009: Take a look at the latest version of this technology, the award-winning RAPHaEL 2. End update.
As far as science-fictional predecessors are concerned, consider the prosthetic hand that Luke Skywalker gets in Star Wars after an argument with his father.
(Luke Skywalker tests his new bionic hand)
Here is one robotic hand story for each of your fingers: